The Electrostatic Interlayer Forces of Layer Structure Minerals

Abstract Using a simple ionic model, the energy necessary to expand a layer structure by a certain distance can be calculated. This has been done for a series of 15 structures including hydroxides, 2"1 and 1:1 structures ofvarious types. Plots of energy versus eparation distance show three major groups which have common bonding properties. For large separations, the group with the strongest interlayer bonds contains the brittle micas, the hydroxides, and the 1:1 structures. Intermediate bonding structures are the normal micas and the weakest bonds occur in the zero layer charge 2:1 structures. The relative nergies needed for a given separation are not constant so that for small separations the zero layer charge structures such as talc and pyrophyllite are more strongly bonded than the normal micas. These groupings correlate very well with the expandability of the structures by water and other substances. It is proposed that his approach to the study of the layer structures will provide a simple theory explaining the expansion properties of layer silicates

Crystal structures of ideal, ordered two-layer micas /

In minerals exhibiting cation disorder, the variation in crystal structure environments can be studied by constructing model structures for all possible cation distributions. The model structures are constructed using known interatomic distances with the computer algorithm DLS (distance least squares). For two-layer mica polytypes, the number of possible ways of distributing Si and Al over the 16 tetrahedral sites is large: 1820 for Si/Al = 3 (as in muscovite) and 12,870 for Si/Al = 1 (as in margarite). It is not feasible to compute DLS structures for all these models, so both populations have been sampled on a random basis to provide 100 cases each for muscovite 2 M sub 1 and margarite 2 M sub 1."Terrestrial Sciences Laboratory Project 8607.""ADA017044 (from http://www.dtic.mil).""5 September 1975."Includes bibliographical references (page 9).In minerals exhibiting cation disorder, the variation in crystal structure environments can be studied by constructing model structures for all possible cation distributions. The model structures are constructed using known interatomic distances with the computer algorithm DLS (distance least squares). For two-layer mica polytypes, the number of possible ways of distributing Si and Al over the 16 tetrahedral sites is large: 1820 for Si/Al = 3 (as in muscovite) and 12,870 for Si/Al = 1 (as in margarite). It is not feasible to compute DLS structures for all these models, so both populations have been sampled on a random basis to provide 100 cases each for muscovite 2 M sub 1 and margarite 2 M sub 1.Mode of access: Internet

Chemical and mineralogical characteristics of French green clays used for healing

The worldwide emergence of infectious diseases, together with the increasing incidence of antibiotic-resistant bacteria, elevate the need to properly detect, prevent, and effectively treat these infections. The overuse and misuse of common antibiotics in recent decades stimulates the need to identify new inhibitory agents. Therefore, natural products like clays, that display antibacterial properties, are of particular interest. The absorptive properties of clay minerals are well documented for healing skin and gastrointestinal ailments. However, the antibacterial properties of clays have received less scientific attention. French green clays have recently been shown to heal Buruli ulcer, a necrotic or 'flesh-eating' infection caused by Mycobacterium ulcerans. Assessing the antibacterial properties of these clays could provide an inexpensive treatment for Buruli ulcer and other skin infections. Antimicrobial testing of the two clays on a broad-spectrum of bacterial pathogens showed that one clay promotes bacterial growth (possibly provoking a response from the natural immune system), while another kills bacteria or significantly inhibits bacterial growth. This paper compares the mineralogy and chemical composition of the two French green clays used in the treatment of Buruli ulcer. Mineralogically, the two clays are dominated by 1Md illite and Fe-smectite. Comparing the chemistry of the clay minerals and exchangeable ions, we conclude that the chemistry of the clay, and the surface properties that affect pH and oxidation state, control the chemistry of the water used to moisten the clay poultices and contribute the critical antibacterial agent(s) that ultimately debilitate the bacteria

Application of principal components analysis to the study of silicate crystal structures /

Principal components analysis (PCA) is a quasi-statistical technique for transforming a given set of variables or observations into a new set of linearly transformed variables. The new set has the advantage that most of the variance of the original observations can be accounted for with fewer variables, thus simplifying interpretation of the variance. PCA has been applied to (1) micas using only interatomic distances and (2) clinopyroxenes using both interatomic distances and angles. In all cases, at most three new variables were necessary to account for 90 percent or more of the original total variance. Each of these new variables can be interpreted in terms of distortions of the crystal structures of the two groups of minerals. One of the advantages of PCA is the quantitative evaluation of specific crystal structure distortions."Terrestrial Sciences Laboratory Project 8607.""ADA017043 (from http://www.dtic.mil).""14 July 1975."Includes bibliographical references (pages 53-54).Principal components analysis (PCA) is a quasi-statistical technique for transforming a given set of variables or observations into a new set of linearly transformed variables. The new set has the advantage that most of the variance of the original observations can be accounted for with fewer variables, thus simplifying interpretation of the variance. PCA has been applied to (1) micas using only interatomic distances and (2) clinopyroxenes using both interatomic distances and angles. In all cases, at most three new variables were necessary to account for 90 percent or more of the original total variance. Each of these new variables can be interpreted in terms of distortions of the crystal structures of the two groups of minerals. One of the advantages of PCA is the quantitative evaluation of specific crystal structure distortions.Mode of access: Internet

An electron-optical investigation of soil clay minerals and soil stabilizing agent reactions /

Characterization of reference clay mineral standards was accomplished by use of the scanning electron microscope (SEM), X-ray diffraction, and energy dispersive X-ray analysis. Experiments were conducted to determine the reactions between these clay minerals and lime which was used as a soil stabilizing agent. Examination of clay minerals visually by use of the SEM offers a partial examination of the irreactivity with soil stabilizing agents. Both surface area and surface roughness increase while there is an apparent decrease in the crystallinity of the clay minerals examined in the following order; Kaolinite group, Illite group, and Montmorillonite group. Reactions were studied of several soil clay minerals with various proportions of Ca(OH)2 and both with and without contact with the air. The major product of the reactions is calcite with smaller amounts of the material 3CaO . Al2O3 . CaCO3 . LlH2O. Scanning electron microscopy of the reacted materials shows a rough, 'corroded' surface on the clays as well as the formation of small single crystals of calcite and Ca(OH)2. Experimental studies showed that the problems of swelling soils can be alleviated by a double application Ca(OH)2 under proper moisture conditions. (Author)."Terrestrial Sciences Laboratory Project ILIR.""ADA015738 (from http://www.dtic.mil).""14 July 1975."Includes bibliographical references.Characterization of reference clay mineral standards was accomplished by use of the scanning electron microscope (SEM), X-ray diffraction, and energy dispersive X-ray analysis. Experiments were conducted to determine the reactions between these clay minerals and lime which was used as a soil stabilizing agent. Examination of clay minerals visually by use of the SEM offers a partial examination of the irreactivity with soil stabilizing agents. Both surface area and surface roughness increase while there is an apparent decrease in the crystallinity of the clay minerals examined in the following order; Kaolinite group, Illite group, and Montmorillonite group. Reactions were studied of several soil clay minerals with various proportions of Ca(OH)2 and both with and without contact with the air. The major product of the reactions is calcite with smaller amounts of the material 3CaO . Al2O3 . CaCO3 . LlH2O. Scanning electron microscopy of the reacted materials shows a rough, 'corroded' surface on the clays as well as the formation of small single crystals of calcite and Ca(OH)2. Experimental studies showed that the problems of swelling soils can be alleviated by a double application Ca(OH)2 under proper moisture conditions. (Author).Mode of access: Internet